This invention relates generally to ion-optical lens systems, and more particularly, to a large aperture ion-optical lens system wherein spherical and chromatic aberrations, as well as other errors, are corrected with the use of a defocusing lens system, which may be of the magnetic or electrostatic type, arranged in combination with a focusing lens system.
Ion focusing in most ion-optical systems utilizes magnetic or electric dipoles or quadrupoles, or electrostatic grids. Characteristically, conventional dipoles and quadrupoles are not characterized by azimuthal symmetry, and therefore have a relatively poor aspect ratio in the form of opening aperture-to-length. Accordingly, these known system elements impose severe restraints upon the angular acceptance (f/#) of the ion-optical system.
In addition to the poor aspect ratio and constrained angular acceptance, the mechanical construction and orientation of such dipole and quadrupole lens systems renders alignment thereof to be difficult. Moreover, such systems do not possess simple optical properties, such as simple ion orbits, ion focusing, and aberrations.
Another type of system which has been used in the art includes grid-type lenses which are arranged in the vicinity of the ion beam path. Such grid-type systems, however, introduce unwanted background noise since some of the ions will strike the grid. Accordingly, such systems are not acceptable for many applications.
It is, therefore, an object of this invention to provide an ion-optical system having a large aperture.
It is another object of this invention to provide a system having a large aperture for controlling a beam of energetic ions.
It is also an object of this invention to provide a simple and economical large aperture ion-optical system which is compact.
It is a further object of this invention to provide a large aperture lens system which can be corrected for spherical aberrations.
It is additionally an object of this invention to provide a large aperture lens system which can be corrected for chromatic aberrations.
It is yet a further object of this invention to provide a large aperture lens system which provides improvement in resolution and efficiency (i.e., collecting power).
It is also another object of this invention to greater than provide a large aperture lens system which operates with reduced background noise.
It is yet an additional object of this invention to provide a large aperture lens system which can be employed in multiple applications, such as mass spectrometers, gas analyzers, leak detectors, ion implantation devices, ion sources, ion accelerators, mass separators, ion spectrometers, ion microprobes, radiation therapy, electron microscopes, ion-optical devices, etc.
It is still another object of this invention to provide a large aperture lens system which does not employ wire grids or metal foils.
It is a yet further object of this invention to provide a large aperture lens system which is useful in focusing energetic ions in the range of approximately between tens of keV to tens of MeV.
It is also a further object of this invention to provide a large aperture lens system which is operable in a non-dispersive, achromatic mode.
It is additionally another object of this invention to provide a large aperture ion-optical lens system which has high angular acceptance and collecting power.
A still further object of this invention is to provide a large aperture ion-optical lens system which can focus positive and negative ions simultaneously.
An additional object of this invention is to provide a large aperture ion-optical lens system which provides full symmetry around the optical axis.
Another object of this invention is to provide a lens system which can provide precise focusing of energetic ions having energy in the range of approximately 10 to greater than 500 MeV, and which is useful in cancer therapy.
A yet further object of this invention is to provide a lens system which can operate in special modes, such as with large angular magnification to provide a sharp focus at a specific location, such as the site of a tumor, while minimizing radiation of adjacent tissue since the beam is greatly defocused elsewhere.